The present invention relates to the supervision of structure elements such as rotor blades; and more particularly, the invention relates to monitoring the gas pressure on such blades, pertaining, e.g., to a helicopter.
The structural integrity of the rotor blades of, e.g., a helicopter is of vital importance for the safety of such aircraft; therefore, they have to be monitored and supervised during flight. The supervision uses a pressure transducer on a blade (one per blade), an inductive transmission path from rotating to stationary parts of the equipment and from there, e.g., to the cockpit, or the like, to trigger a warning lamp in case of any undue pressure drop. Unfortunately, such a monitoring system is necessary because the rotor blades may not be sufficiently reliable, even when checked prior to takeoff.
A major problem within the system outlined above is caused by the transmission of the measuring signals from rotating to stationary parts. Slip rings, collector rings, or the like, are not sufficiently reliable due to strong vibrations to which the aircraft is subjected. Another approach involves the utilization of radioactive elements which are shielded as long as the rotor remains without defect, while defects are used to offset some of the shielding. This approach is objectionable for a number of reasons, such as health and outside interference in the case of military aircraft.
Another approach is the use of a rotational transformer. The primary winding rotates with the propellor, the secondary winding is stationary, and the windings are constructed in such a manner that signals can be transmitted during and in spite of the rotation. Concerning the inductive transmission of signals between a stationary and a rotating member, see, for example, German patent 1,616,431. Unfortunately, the rotor construction in a helicopter, including particularly the bearings, and so forth, does not permit the inclusion of such a transformer; there just is not enough space available. One would have to change the entire propeller construction as to its bearings, and related parts, which creates too much of a problem.